An empty sequence is not allowed as the first argument of z:index()

See #141, release log:

• 04a70ef by @yegor256: #141 test eva
• 1061273 by @yegor256: #141 tested
• fc25c6b by @yegor256: #141 summary in another file
• 927bafb by @yegor256: #138 more tests
• 97d2d46 by @yegor256: Merge pull request #140 from z...

Released by Rultor 2.0-SNAPSHOT, see build log